In an effort to determine the risk involving exposure to nitrous oxide (N2O), this research proposal is designed to define the psychomotor impairment related to the exposure of humans to N2O. The work during the first year of this project will involve constructing a testing chamber where the concentration of N2O can be carefully controlled and monitored. A forced choice, audiovisual reaction time testing apparatus for evaluating the psychomotor impairment will be designed and its accuracy and sensitivity will be evaluated. Following development of this testing environment, healthy young adults will be exposed to various concentrations of N2O and the dose dependent decrease in function will be determined. The lowest concentration of N2O that induces impairment (threshold) will also be determined. This initial work will serve as baseline data for the studies of the second and third year of the project. The changes in threshold and dose vs. impairment relationship will be determined following prolonged exposure to low concentrations of N2O (a situation similar to occupational exposure) to repeated high concentrations of N2O (a situation similar to recreational exposure). Changes in the rate of recovery following N2O exposure will be determined following therapeutic exposures of long and short duration. Recovery will be similarly evaluated following different concentrations of therapeutic exposure. The results of this study will be valuable in constructing guidelines for the safe use of N2O in dentistry.